Actually filtering tabs (instead of just searching for a keyword) is useful when you're trying to "clean up" a large session.
Consider the case where you have a bunch of wikipedia tabs open, and you want to move them all into their own group. If you could filter for wikipedia and select multiple tabs (with ctrl/shift clicking, etc) then you could drag them all into their own group to quickly "clean up" your session and pull out the things that are important and close the things that aren't.
Also, if you implement your own filtering function (instead of relying on chrome's) it lets you implement more powerful filtering like logical AND, OR, NOT for filtering/search criteria.
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